We propose to continue our search for measles virus genes in Multiple Sclerosis and controls, and to extend this analysis to other viruses that might reasonably be expected to gain access to the human central nervous system during childhood infection. As in the past we will use primarily in situ hybridization to detect virus genes, but we describe a new screening method that we hope will complement in situ hybridization by allowing us to sample larger areas of the central nervous system. We also propose a systematic analysis of virus life cycle in vivo that should shed some light on mechanisms of chronic measles virus infection. This analysis will employ hybridization with region and strand specific probes; quantitative measurement of viral proteins with radiolabelled monoclonal antibody to viral gene products; and a combined fluorescence-in situ hybridization technique with monoclonal antibodies to a subset of nerual cells and virus specific probes.